1. Technical Field
The present invention relates to an automatic pressure-relieving apparatus for a suction pump and, more particularly, to a device that functions for relieving the vacuum state inside a suction pump being filled with oil.
2. Description of Related Art
FIG. 10 provides a schematic cross sectional view of a conventional suction pump. To operate such conventional suction pump, a user can pull a pull rod 60 to exhaust air in the cylinder 61 of the suction pump through an air channel 62 and a piston tube 63, whereby while the air in an oil reservoir 611 thereof is exhausted out gradually, suction can be generated in virtue of the nearly vacuum state in the oil reservoir. At this time, by an oil pipe 64 that communicates the oil reservoir 611 and external oil to be collected, said suction helps draw the external oil into the oil reservoir 611 of the cylinder 61 gradually. When the oil reservoir 611 is about to be filled, a float 65 provided in the cylinder 61 is lifted by the raising oil surface and finally a sealing end 651 of the float 65 comes to block an opening 621 situated between the air channel 62 and the oil reservoir 611. Subsequently, when the pullrod 60 is pulled, air existing between the piston tube 63 and the air channel 62 can be almost entirely exhausted out and a near vacuum state can be consequently formed between the piston tube 63 and the air channel 62. Under such vacuum state, the sealing end 651 of the float 65 presses even closer onto the opening 621, and the pullrod 60 now becomes immovable. Thus, a user can be informed that the cylinder 61 is filled with oil and he can press a relief valve 66 manually to let external air enter the air channel 62, so as to release the vacuum state between the piston tube 63 and the air channel 62.
Foresaid conventional technique regarding prevention of oil overflowing problem and pressure-relieving operation depends on the user's estimation of whether the pullrod 60 can be further pulled and his manual operation of pressing the relief valve 66 to release pressure. However, in addition to the inconvenience caused by the manual pressure relieving operation, another problem of this method is that if the user continuously pulls the pullrod 60 under the vacuum state with excessive force, the inner components of the pump such as the sealing end 651 may be damaged; consequently, the contained oil may undesirably overflow into the air channel 62 and this in turn induces contamination.
Hence, for more convenient operation of a suction pump, a need exists for an apparatus that automatically conducts pressure-relieving operation when the pump is filled with oil.